Electrophotographic reproduction material



3,l?4,854 Patented Mar. 23, 1965 3,174,354 ELECTRGPHQTOGRAPHEC REPRODUCTION MATERIAL Hans Rainer Stiimpt and Wiihelm Neugebauer, Wiesbaden-Biebrich, Germany, assignors, by mesne assignments, to Azoplate Corporation, Murray Hiil, NJ. No Drawing. Filed Apr. 6, 1960, Ser. No. 20,283 Claims priority, application Germany, Apr. 8, 1959,

34 Claims. c1. 96-4) Among modern reproduction processes the electrophotographic process, also known as xerography, is becoming of increasing practical importance. This dry process is of particular interest in certain fields, for example, office duplicating, and it consists in the application to a material consisting of a support and a photoconductive insulating layer adherent thereto of an electrostatic charge which imparts to the insulating layer the property of light-sensitivity.

Material made light-sensitive in this way can be used for the production of images by electrophotographic means. It is exposed to light beneath a master, so that the electrostatic charge is leaked away in the parts of the layer struck by light. The invisible latent electrostatic image thereby produced is made visible (developed) by powdering over with a developer consisting of a mixture of a carrier with a toner. The carrier used may be, e.g. tiny glass balls, iron powder or other inorganic substances or even organic substances. The toner consists of a resin-carbon black mixture or of pigmented synthetic resin of a grain size of 1-100p, preferably -30 The image is then made permanent (fixed) by the application of heat to the support.

Materials known for the preparation of the photoconductive insulating layers required for the above-described process include selenium, sulphur, zinc oride, and also organic substances such as anthracene or anthraquinone. Consideration has also been given to a method of preparation of the photoconductive insulating layers whereby the photoconductive substances in association with binders are dispersed in solvents and the resultant dispersions applied to supports, primarily metal foils, and dried. However, the photoelectrically sensitizable m..- terial thus obtained has not yet satisfied the extensive demands made of modern duplicating material regarding range of use, reliability, simplicity in handling and, not least in importance, light-sensitivity and storageability qualities.

It has now been found that unexpectedly successful photoelectrically sensitizable layers, with a surprising range of practical applications, are produced it, as photoconductive substances, compounds are used which correspond to the general formula in which X is O, S, or NR and R R R and R and R can be hydrogen, alkyl, aryl or substituted aryl, at least two of R R R and R being aryl or substituted aryl.

The compounds to be used in accordance with the invention as photoconductive substances are aryl furans or aryl thiophenes or aryl pyrroles. Compounds corresponding to the above formula which contain substituted aryl radicals, e.g. aryl radicals substituted by halogen, amino groups, alkyl or alkoxy groups are also included in the photoconductive substances of the invention. The presence of nitro or nitroso groups reduces the suitability of the aryl turans, aryl thiophenes and aryl pyrroles of the invention, or renders them completely unsuitable for the invention.

The compounds corresponding to the above general formula are colorless and give very homogeneous layers of very good shelf life.

For the preparation of the photoconductive insulating layers, it is advantageous for the aryl furans, aryl thiophenes and aryl pyrroles to be used in solution with organic solvents, e.g., benzene, acetone, methylene chloride, glycol monomethylether, and the like. Mixtures of solvents may also be used. Also, it is possible for the aryl furans, aryl thiophenes and/ or aryl pyrroles to be used in association one with another or with other organic photoconductive substances.

As has further been discovered, it may be an advantage in the production of the photoconductive insulating layers if resins are used in association with the aryl furans, aryl thiophenes and aryl pyrroles of the invention. The following are exemplary: natural and synthetic resins, cg. balsam resins, phenol resins modified with colophony and other resins of which colophony constitutes the major part, coumarone resins and indene resins and the substances covered by the collective term synthetic lacquer resins, which according to the Kunststotftaschenbuch (Plastics Pocket Book), published by Saechtling-Zebrowski (11th addition, 1955, page 212 et seq.) include processed natural substances such as cellulose ethers; polymers such as polyvinyl chlorides, polyvinyl acetals, polyvinyl acetates, polyvinyl ethers, polyacrylic and polymethacrylic esters, as also polystyrene and isobutylene; polycoudensates, e.g. polesters, such as phthalate resins, alkyd resins, maleic acid resins, maleic acid/ colophony/ mixed esters of higher alcohols, phenol-formaldehyde resins, particularly colophonymodified phenol-formaldehyde condensates, urea-formaldehyde resins, melamine-formaldehyde condensates, aldehyde resins, ketone resins, of which particular mention is to be made of those available under the name of AW 2 resins, Xylene formaldehyde resins and polyamides; and polyadducts, such as polyurethanes.

If the aryl iurans, aryl thiophenes and aryl pyrroles corresponding to the above general formula are used in association with resins, the proportion of resin to photoconductive substance can vary very greatly, but the content of photoconductive substance should be at least 20%. T he use of mixtures of approximately equal parts of resin and photoconductive substance has been found advantageous; if such mixtures of about equal parts of resin and photoconductive substance are used, the solutions, on drying, generally give transparent colorless layers which physical testing shows to be solid solutions.

The base materials used may be any that satisfy the requirements of xerography, e.g., metal or glass plates, paper or plates or foils made of electroconductive resins of plastics, such as polyvinyl alcohol, polyamides, and polyurethanes. Generally, electroconductive supports are suitable for the purposes of the present invention. In the sense of the present invention, the term electroconductive support comprises materials having a specific conductivity higher than 10- ohm -cm. preferably higher than 10 ohm 'cm.- If paper is to be used as support for the photoconductive layer, pretreatment of the paper against penetration of the coating solution is advisable, e.g., with methylcellulose in aqueous solution or polyvinyl alcohol in aqueous solution or with a solution in acetone and methylethylketone of a copolymer of acrylic acid methyl ester and acrylonitrile or with solutions of polyamides in aqueous alcohols. Aqueous dispersions of substances suitable for the pretreatment of the paper surface may also be used.

The solutions of the aryl furans, aryl thiophenes and aryl pyrroles to be used in accordance with the invention, with or without the resins, are applied to the supports in the usual manner, for example by spraying, by direct application, by means of rollers and the like, and then dried in a manner such that a homogeneous photoconductive layer is produced on the support.

After an electrostatic charge has been applied, by means of, for example, a corona discharge, the layer can be used, preferably, with long-wave UV. light of 3600-4000 A. for electrophotographic image production. Very short exposure under a master to a high pressure mercury lamp will give good images.

The further discovery has been made that the lightsensitivity to the visible range of the spectrum of the photoconductive layer can be highly improved. by the addition of dyestuffs. The amount of sensitizer to be added to the photoconductive substance is generally up to 3% of the photoconductive substance. However, even very small quantities, e.g., less than 0.01%, have con siderable effect. As sensitizers, dyestuffs in particular are suitable, for the readier identification of which the number is given under which they are listed in Schultz Farbstofit'tabellen (7th edition, 1st vol. 1931). The following are given as examples of effective sensitizers: triarylmethane dyestuffs such as Brilliant Green (No. 760, p. 314-), Victoria Blue B (No. 822, p. 347), Methyl Violet (No. 783, p. 327), Crystal Violet (No. 785, p. 329), Acid Violet 6B (No. 831, p. 351); xanthene dyestuffs, namely rhodamines, such as Rhodamine B (No. 864, p. 365), Rhodamine 6G (No. 866, p. 366), Rhodamine G Extra (No. 865, p. 366), Sulphorhodamine B (No. 863, p. 364) and Fast Acid Eosin G (No. 870, p. 368), as also phthaleins such as Eosin S (No. 883, p. 375), Eosin A (No. 881 p. 374), Erythrosin (No. 886, p. 376), Phloxin (No. 890, p. 378), Bengal Rose (No. 889, p. 378), and Fluorescein (No. 880, p. 373); thiazine dyestuffs such as Methylene Blue (No. 1038, p. 449); acridine dyestuffs such as vAcridine Yellow (No. 901, p. 383), Acridine Orange (No. 908, p. 387) and Trypaflavine (No. 906, p. 386); quinoline dyestuffs such as Pinacyanol (No. 924, p. 396) and Cryptocyanine (No. 927, p. 397); quinone dyestuffs and ketone dyestuffs such as Alizarin (No. 1141, p. 499), Alizarin Red S (No. 1145, p. 502), and Quinizarine (No. 1148, p. 504); cyanine dyestuffs, e.g. Cyanine (No. 921, p. 394).

The production or" images by electrophotographic means is carried out as follows: when the photoconductive layer has been charged positively or negatively, by means of for example, a corona discharge with a charging apparatus maintained at 6000 volts, the support, e.g. paper or aluminum foil or plastic foil, with the sensitized coating, is exposed to light under a master or by episcopic or diascopic projection and is then dusted over in known manner with a developer consisting of a mixture of a carrier and a toner. The carriers used may be, for example, tiny glass balls, iron powder or other inorganic substances or even organic substances. The toner consists of a resin-carbon black mixture or a pigmented resin of a grain size of 1 to 100 preferably 30/.L. The finely distributed toner particles adhere to the parts of the coating not struck by light during the exposure, and a positive image becomes visible if the photoconductive layer was negatively charged and the toner carrying a positive polarity is used. With the same toner only by changing the polarity of the corona discharge, there can be obtained also reversal images of the master. The image that now becomes visible can easily be wiped off. It therefore has to be fixed; it can, for example, be briefly heated by means of an infrared radiator. The temperature required is less if the heat treatment is carried out in the presence of vapors of solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol. The fixing of the powder image can also be done by steam treatment. Images characterized by good contrast are produced.

After being fixed, these electrophotographic images can be converted into a printing plate, if a hydrophilic foil, e.g. paper or plastic foil, is used as support and the support and the fixed image are wiped over with a solvent for the photoconductive layer, e.g. alcohol or acetic acid, then wetted with Water and inked up in known manner with greasy ink. In this way, positive printing plates are obtained which can be set up in an offset machine and used for printing. Very long runs are obtained.

If transparent supports are used, the electrophotographic images can also be used as masters for the production of further copies on any type of light-sensitive sheet. In this respect the photoconductive compounds of the invention are superior to the substances used hitherto, such as selenium or zinc oxide, inasmuch as the latter give only cloudy layers.

If translucent supports are used for photoconductive layers such as are provided by the invention, reflex images can be produced also. Before being fixed, the image formed by the powdering process may, without dimculty, be transferred in known manner by electrical charging to another support and fixed thereon by heat. In this case, the transfer material, e.g. a sheet of paper, is laid onto the unfixed powder image and charged with a corona discharge having the same polarity as the original charge of the now developed electrostatic image, so that the powder image is attracted by the paper and thereon fixed by heating.

Furthermore, the photoconductive layers of the invention have another important advantage in that they can be charged positively as well as negatively. This has the advantage, that with the same developer, only by changing the polarity of the corona charging device, it is possible to obtain direct and reversal copies from the same master. The photoconductivity of the photoconductors according to the present invention is superior to that of known photoconductive substances, such as anthracene, benzidine, and r rth-raquinone.

Exemplary of the compounds to be used in accordance with the invention are the following:

Formula 1 Q @U-Q Formula 2 Formula 3 QM Q Formula 4 Formula 5 Formula 6 Formula 7 Formula 8 Formula 9 Formula 10 Formula 11 Formula 12 Formula 1 Formula 1 @N O Formula 1 Formula 1 Formula 17 Formula 18 Formula 19 Formula 2 Formula 2 8 Formula 23- Formula 30 CH -O Cl 1 I 1 C) -O U 1 (I: 1 NH Formula 24 HTO C Those compounds corresponding to the general formula which have not already been described in the literature may be prepared as follows. (CHS)2N Q 1,4-diaryl-butandione-(1,4) or l,2,4-triaryl-butandione- (1,4) compounds are used as starting materials. These Formula 25 are reacted with:

(l) Concentrated sulphuric acid or polyphosphoric acid for the preparation of aryl furans, or

(2) Phosphorus trisulphide or phosphorus pentasulphide (OH) for the preparation of aryl thiophenes, or

3 2 N (3) Formamide for the preparation of aryl pyrroles, the

reaction in this last case being at the boiling point.

The method of preparation is illustrated in the following examples: 4-phenyl-1,2-bis-(4-chlorphenyl)furan, corresponding to Formula 22, is obtained if 4 g. of 4-phenyl-l,2-bis-(4- Formula 2 chlorphenyl)-butandione-(1,4) are dissolved Without heating in 25 ml. of concentrated sulphuric acid and the reaction mixture is allowed to stand for one hour and is then poured on ice. The reaction product is separated by suction filtration, Washed with Water, and recrystal- O1-Q s lized from a mixture of ethanol and glycol monomethyl NH ether. Melting point: l32l33 C.

1,2-diphenyl-4-naphthyl- (2 -thiophene, corresponding Formula 27 35 to Formula 6, is obtained if 5 g. of 1,2-diphenyl-4-naphthyl-(2')-butandione-( 1,4) and 2 g. of phosphorus trisulphide are ground together and the mixture heated for a short time to 150 C. and then cooled. The reaction mass CH L is recrystalized a number of times from ethanol. Meltm 3 0 3 mg point: 126128 C.

2,3-diphenyl-5- (4'-methylphenyl) -pyrrole, correspond- Formula 28 ing to Formula 11, is obtained if 5 g. of 1,2-diphenyl- 4(4-methylphenyl)-butandione-(1,4) are boiled under I reflux for 2 /2 hours With 50 ml. of formamide and the re- 3 O action mixture is then cooled. The reaction product is a A) separated by suction filtration and recrystallized from H3 methanol. Melting point: 127-l28 C.

Formula 29 2,3,5 triphenyl-1-(4'-methoxyphenyl)-pyrrole, corresponding to Formula 14, is obtained if 7.5 g. of 1,2,4-triphenyl-butandione-(1,4), 3.1 g. of 4-ami11o-1-methoxybenzene and 30 ml. of glacial acetic acid are boiled under Q reflux for 3 hours. The reaction product is separated by suction filtration from the cooled reaction mixture and n recrystallized from a mixture of ethanol and dioxane.

(L NH Melting point: 148150 C.

HFO The table below indicates the reactants required:

a b c d e f Formula g)??? h ii iid i d zl g Second Reactant Solvent l g l iis 5 -126 -ldiphenyl--naphthyl-(2)- 5,3505%. sulphuric acid Ethanol/dioxane.

6 126-128 idiphenyl-e-naphthyl-(2)- 2Plgpsphorus trisulphide None Ethanol.

7 188-189 tlidiphenyl-l-naphthyl-(2)- gboglr iamiden Benzene.

9 184-185 Lgdiphenyl-tnaphthyl-(2) sk'gnlifiobeuzene lCglizxclial acetic acid- Ethanol.

10 88-91 %,2:dipl1enyl-(4-methylphenyl)-. ggcsphorustrisulphide None D0.

11 127-128 %,2- dipheny1-(4-methylpheny1)-. go r n lamidan Methanol.

llrg-g'iphenyl-t(4-methylphenyl)- g-grninonaphthalene gliglial acetic acid- Acetic acid ethylester. gdiphenyl-(4-methoxypheny1)- EQorfinamida. Ethanol. 1,2,4-triphenyl 4-arnino-1-metl1oxybenzcne Glacial acetic acid Ethanol dioxane. 7.5 g. 3.1 g. 30 m1.

a b c d e f Melting Substitution of the Recrystallization Formula P oicnt, butandione-(L4) Second Reactant Solvent solvent 15 148-151 2,4-gipheinyl-l-(4-dimethylamino- Oonc. sulphuric acid Ethanol.

p eny 3 g. 20 ml. 16 116-117 2,4-il1ipheinyl-1-(4-dirnethylamino- Phosphoruspentasulphide Acetone.

p eny 17. 157-159 2-phenyl-1-(4-dimethyl-amino- Conc. sulphuric acid Benzene.

phenyl)-4-naphthyl-(2)- 3.5 g. 30 ml. 18 172-175 2-phenyl-1- -dimethylammo- Aminobenzene Ethanol/dioxanc.

2 phenyl)-4-naphthyl-(2)- m g. 19 124-125 2,4-giphe;1yl-1-(4-diethyl-amino- Cone. sulphuric acid Ethanol.

D y 2.4 g. 30 ml. 20 132-133 Z-phenyl-l-(4-diethyl-amino- Cone. sulphuric acid Do,

phenyl)-4-naphthyl-(2)- 2.2 g. ml. 21 177-178 2-phenyl-1-(4-dicthyl-a1nino- Aminobenzene.. Glacial acetic acid, Benzene.

phenyl)-4-naphthyl-(2)- 2.5 g. 0.6 ml. 10 ml. 22 132-133 4-phenyl-L2-bis-(4-chl0ro-phenyl)- Conc. sulphuric acid Ethanol/Z-methoxyethanol.

4 g. 25 ml. 23 166-167 -phenyl-1,2-bis-(4-ch1oro-phenyl)- Forrilrliamide... Ethanol.

g. 24 150-151 4-phenyl-2-(4-chloro-phenyl)-1- Conc. sulphuric acid Methanol/die); one,

4 (4"-dimethyl-amino-phenyl)- 1 g. m 25 159-160 4-phenyl-2-(4-chloro-phenyl)-l- Z-amino-naphthalene Glacial acetic acid Ethanol.

(4"-dimcthyl-amino-phcnyl)- 1 g. 0.35 g. 6 ml. 26 195-196 1,2-bis-(4-chlorophcnyl)-4-(4- F0rmamide.- Benzene,

methoxy-phenyD- 6 g. 5 ml. 27 127-128 2- (4-chl0ro-phenyD-l-(M-di- Cone. sulphuric acid Ethanol,

rnethylamino-phenyD-4-(4- methoxy-phenyD- 1.5 g 13 ml. 29 213-215 4-phenyl-L2-bls-(3,4-mcthylcne- Formamide Ben 7on0 dihydr0xy-phenyl)- 5 g. 50 ml. 30 4-(4-methoxy-phenyl)-l,2-bis- Formamide M th ol,

(3",4-methylenc-dihydroxyphenyl)- 6.5 g. 50 m1.

Some of the 1,4-butadiones used as starting materials have already been described in the literature.

Those not previously disclosed can be prepared in a manner analogous to the following process for 2,4-diphenyl-1-(4' dimethylaminophenyl)-butadione-(1,4), corresponding to Formula 31,

below.

19 g. of 4-dimethylaminobenzoin, 9 g. of acetyl benzene and 4 g. of finely pulverized potassium hydroxide ing to Formula 31 is 153-154 C.

Other butadiones are as follows:

Formula 31 Formula 32 Formula 33 Cl-O-TH-CH Formula 34 Formula 35 Formula 36 Formula 37 (ll-OCH-CI-n ouOL) (Lo-4015 Formula 38 m-O-cn-om Formula 39 O Hg-O J. TH IH. -CF *6 The following table contains details for the preparation of the 1,4-butadiones:

12 tion is dried. Electrophotographic image :production on this coated paper is as described in Example 1.

Example 3 Melting Potassium Recrystalli- Formula Point, C. Benzom Substitution Second Reactant Hydroxide zation solvent 153-154 4dimethylamin0- tcetylbenzene 31 Ethanol.

1 g. g. g. 176-178 fidimethylaminogacetylnaphthalene .[5 Benzene,

g. g. g. 173-174 4-diethylamiuo- Acetylbeuzene Ethanol.

g. 4.2 g. 0.5 g. 177-178 t diethylaminog-zgcotylnaphthalene Benzene.

1 .2 g. g- 35 135-137 4 4-dicbloro-...., Acetylbenzene Ethanol.

1 g. g. g. 36 166-167 4-dimethylam1no-4- Acetylbenzen Do.

chlorog. 12 g. 2 g. 37 4,4-dlehloroi-methoxyd-acetylben- Do.

zene. 14 g. 7.5 g. 1 g. 38 146-148 4-dimethylamino-4- 4-rneth0xy-1-acetylben- D0.

chlorozene. 18 g. 9.3 g. 1.5 g. 39 148-150 Bis-3,4-metl1ylene-di- Acetylbenzene Do.

hydroxy- 15 g. 6 g. 1 g.

The invention will be further illustrated by reference to the following specific examples:

Example 1 A solution containing 2 g. of the compound corresponding to Formula 3 in ml. of benzene is applied to paper, the surface of which has been treated against the penetration of organic solvents, and dried. A direct image is then produced on the coated paper by the electrophotographic process, the paper being provided with a negative electric charge, by means of a corona discharge, exposed under a master to the light of a high pressure mercury vapor lamp and dusted over with a developer consisting of a mixture of tiny glass balls with a toner. The toner consists of a resin-carbon black mixture which takes on a positive polarity, or of a pigmented resin, which takes on a negative polarity when the developer is used. The particles of the toner have a grain size of 1-10Qu, preferably 5-30 1. The finely divided resin adheres to the parts of the coating not struck by light during the exposure and a positive image becomes visible, if the photoconductive layer is negatively charged and a toner carrying a positive polarity is used. With the same toner, only by changing the polarity of the corona discharge, there can be obtained also negatives of the master. The images obtained are slightly heated and thereby made permanent (fixed). effect, since the paper is brightened by the substance applied.

If a suitable transparent plastic foil or transparent paper is used as a support for the photoelectric coating instead of paper as described above, the image produced is suitable as a reproduction master for the preparation of copies by means of any type of light-sensitive sheet.

Example 2 A solution containing 1 g. of the compound corresponding to Formula 9 and 1 g. of ketone resin, e.g. the Kunstharz AP prepared by the condensation of acetophenone with formaldehyde, in 30 ml. of benzene is applied to paper, the surface of which has been treated against the penetration of organic solvents and the solu- They have good contrast 60 means of a corona discharge, the now sensitized paper is exposed under a transparent positive master to the light of Example 4 1 g. of the compound corresponding to Formula 17, 1 g. of ketone resin, e.g. the Kunstharz AP mentioned in Example 2, and 0.01 g. of Rhodamine B (Schultz Farbstofltabellen, 7th edition, 1st vol. (1931) No. 864) are dissolved in 30 ml. of benzene and the solution is applied to paper and dried. With the coated paper, electrophotographic images can be produced by the process described in Example 1. Images on a blue ground are obtained.

Example 5 0.5 g. of the compound corresponding to Formula 15, 0.5 g. of 4,5-di-(4'-chlorophenyl)-imidazolone-(2) and 1 g. of ketone resin, e.g. the commercially available Kunstharz AP, are dissolved in 30 ml. of a mixture of glycol monomethylether and benzene (1:1). The solution is applied to paper and dried. With the coated paper, electrophotographic images are prepared by the process described in Example 1. Images on pale yellowish ground are obtained.

Example 6 0.5 g. of the compound corresponding to Formula 13,

0.5 g. of 4-phenyl-5 (4'-dimethylamino-phenyl)-imid azolone-(2) and 1 g. of ketone resin, e.g. the commercially available Kunstharz EM, are dissolved in 30 ml. of a mixture of glycol monomethyl ether and benzene (12-1). The solution is applied to pretreated paper. The coated 7 paper, after being charged by a corona discharge, is ex- 7 ground is obtained. It is fixed by heating.

13 Example 7 1 g. of the compound corresponding to Formula 19 and 1 g. of ketone resin, e.g. the Kunstharz SK mentioned in Example 3, are dissolved in 30 ml. of a mixture of glycol monomethyl ether and toluene (1:1). The solution is applied to a superficially roughened aluminum foil and the solvent is evaporated oil. The coating left on the aluminum then adheres firmly to the surface of the foil.

For the preparation of the image, the procedure is as described in Example 1. With a transparent master, a positive image is obtained. The aluminum foil with the fixed electrophotographic image can be converted into a positive printing plate if the aluminum foil is wiped over on the image side with a developer liquid consisting of 8 parts by volume of ethanol, 2 parts by volume of glycol monomethyl ether and 1 part by volume of 10% phosphoric acid, and then rinsed down with water and inked up with greasy ink.

Example 8 A solution containing 1 g. of the compound corresponding to Formula 19 and 1 g. of chlorinated polyvinyl chloride resin, e.g. the resin marketed under the registered trademark Rhenoflex in 30 ml. of a mixture of methyl-ethyl-ketone and toluene (1:1) is applied to pretreated paper. After the solution has dried, the coated paper is used for the production of an electrophotographic image by the process described in Example 1. With a short exposure, a good image on pale yellowish ground is obtained.

Example 9 1. g. of the compound corresponding to Formula 18 and 1 g. of ketone resin, e.g. the Kunstharz EM mentioned in Example 6, are dissolved in 30 ml. of a mixture of benzene with glycol monomethyl ether (1:1). The solution is applied to paper and dried. The coated paper is charged, exposed to light under a transparent master and dusted over with developer powder (in the manner described in Example 1) and then a sheet of writing paper is placed on the unfixed electrophotographic image. The coating is again charged, this time through the back of the writing paper. This second charge must have the same polarity as the first; the image is in this Way transferred to the writing paper and is fixed by slight heating.

It will be obvious to those skilled in the art that many modifications may be made Within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula in which X is selected from the group consisting of O, S, and NR and R R R R and R are selected from the group consisting of hydrogen, alkyl, and aryl groups, at least two of R R R and R being other than hydrogen and alkyl, and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestuff.

2. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula 14 in which R R and R are aryl groups, and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestufi".

3. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula R2C-C-H Iii-( i ("J-R3 s in which R R and R are aryl groups, and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestuff.

4. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula in which R R R and R are aryl groups, and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestuif.

6. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula in which R is an alkylamino group and R and R are aryl groups, and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestuif.

7. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula R.@ l a...

in which R is an alkylamino group and R and R are aryl groups, and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestulf.

8. An electrophotograpnic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula in which R is an alkylamino group and R R and R are aryl groups, and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestutf.

amines 9. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula layer, the latter comprising a compound having the formula and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestuff.

11. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula Q and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestufi.

12. An electrophotograpic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestuif.

13. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula l5 and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestuff.

15. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestufi.

16. An electrophotographic material comprising a conductive support layer and a photoconductive insulating layer, the latter comprising a compound having the formula and a compound selected from the group consisting of a resin and a spectrally sensitizing dyestutf.

17. A photographic reproduction process which comprises electrostatically charging a supported photocon-' ductive insulating layer, exposing the charged material to a light image, and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula Rz-C C-Ra S, NR and R R R R and R are selected from the group consisting of hydrogen, alkyl, and aryl groups,

at least two of R R R and R being other than hydro- 7 gen and alkyl.

18. A process according to claim 17 in which the photoconductive layer contains a resin.

19. A process according to claim 17 in which the photoconductive layer contains a spectrally sensitizing dyestuff. 7

20. A photographic reproduction process which comprises elcctrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image, and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 21. A photographic reproduction process which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image and developing the resulting image with an electroscopic material, the photocouductive layer comprising a compound having the formula in which R R and R are aryl groups.

22. A photographic reproduction process which comprises electrostatically charging a supported photocon- 1 7 ductive insulating layer, exposing the charged material to a light image and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula in which R R R and R are aryl groups.

24. A photographic reproduction process which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula in which R is an alkylamino group and R and R are aryl groups.

25. A photographic reproduction process which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image, and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula in which R is an alkylamino group and R and R are aryl groups.

26. A photographic reproduction process Which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image, and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula in which R is an alkylarnino group and R R and R are aryl groups.

27. A photographic reproduction process which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula Q NEG 28. A photographic reproduction process which comprises electrostatically charging a supported photocon- 18 ductive insulating layer, exposing the charged material to a light image and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 29. A photographic reproduction process which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light imageand developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 30. A photographic reproduction process which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 31. A photographic reproduction process which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 3 2. A photographic reproduction process which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula 33. A photographic reproduction process which comprises electrostatically charging a supported photoconductive insulating layer, exposing the charged material to a light image and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula i9 20 34. A photographic reproduction process which com- 2,768,077 10/56 Neugebauer et a1. 96-115 prises electrostatically charging a supported photoconduc- 2,352,503 9/58 Long et a1. 2512 301 2 tive insulating layer, exposing the charged material to 21 2,915,534 12/59 L 1; 1 252-3011,; light image and developing the resulting image with an 2354391 9 Cl 9 1 electroscopic material, the photoconductive layer com- 5 3,041,165 6/62 Sus et 1;

prising a compound having the formula FOREIGN PATENTS 201,416 4/56 Australia. 563,045 6/58 Belgium.

10 1,177,936 12/58 France. f 1,188,600 3/59 France.

OTHER REFERENCES Hannay: Semi Conductors, Rheinhold (1959), pages References Cited by the Examiner NORMAN G. TORCHIN, Primary Examiner.

UNITED STATES PATENTS PHILIP E. MANGAN, Examiner. 1,587,269 6/26 Beebe et a1 96-1l5 20 2,297,691 1 0/42 Carlson 96--1 

1. AN ELECTROPHOTOGRAPHIC MATERIAL COMPRISING A CONDUCTIVE SUPPORT LAYER AND A PHOTOCONDUCTIVE INSULATING LAYER, THE LATTER COMPRISING A COMPOUND HAVING THE FORMULA 